<!-- test伪类和伪元素 -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        /* a 变红 */
        p:first-child {
            color: red;
        }
        /* a b 变黄 */
        p::first-letter {
            color: yellow;
        }
    </style>
</head>
<body>
    <div>
        <p>a</p>
        <p>b c</p>
    </div>
</body>
</html>